Up-conversion of a video signal format with expansion of active portion of video field

ABSTRACT

A digital video signal is real-time converted from a conventional definition format, such as 525 lines, 60 field/s, 2:1 interlace, with a 4:3 aspect ratio and 720×486 active pixels, to a high definition format, such as 1125 lines, 60 field/s, 2:1 interlace, with a 16:9 aspect ratio and 1920×1035 active pixels by writing the pixels of the conventional definition fields to alternate field stores at the conventional definition format pixel rate; by formed intermediate frames in the high definition format by reading pixels from the field store which is not being written at the high definition pixel rate and adding background pixel data between the lines of the read pixels and between the fields of the read pixels; by translating the pixels of the intermediate image, if necessary; and by expanding the image so that the originating pixel data extends across the whole frame in at least one direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to up-conversion of digital video signals from aconventional format to a high-definition format.

2. Description of the Prior Art

High definition digital video is becoming increasingly popular, andcommon formats for the video signals are:

SMPTE 240 M format, which is characterised by 1125 lines, 60 field/s,2:1 interlace, with a 16:9 aspect ratio and 1920×1035 active pixels perframe; and

European HDTV format, which is characterised by 1250 lines, 50 field/s,2:1 interlace, with a 16:9 aspect ratio and 1920×1152 active pixels perframe.

More and more material is being originated in these formats forprocessing and/or distribution in them. However, there is obviously agreat bulk of material which has been originated, or still needs to beoriginated, in conventional definition format, and there is adesirability to be able to up-convert such material to high definitionformat so that it can be integrated with other high definition materialand/or so that it can be distributed in high definition format. Examplesof conventional definition digital formats are:

CCIR 601 525-line format, which is characterised by 525 lines, 60field/s, 2:1 interlace, with a 4:3 aspect ratio and 720 ×486 activepixels per frame;

CCIR 601 625-line format, which is characterised by 625 lines, 50field/s, 2:1 interlace, with a 4:3 aspect ratio and 720 ×576 activepixels per frame;

4fsc 525 D2 format, which is characterised by 525 lines, 60 field/s, 2:1interlace, with a 4:3 aspect ratio and 768×486 active pixels per frame;and

4fsc 625 D2 format, which is characterised by 625 lines, 60 field/s, 2:1interlace, with a 4:3 aspect ratio and 948×576 active pixels per frame.

Problems associated with such up-conversion include dealing with thechange of aspect ratio from 4:3 to 16:9, in addition to dealing with thechanges of resolution, which are different in the horizontal andvertical directions, and providing temporal conversion in the case of achange in field rate.

OBJECT AND SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided an apparatus for up-converting a digital video signal from afirst definition format to a second high-definition format, comprising:storage means which can store an input field/frame of pixel data in thefirst format; storage control means for controlling the storage means tooutput the stored pixel data together with dummy data as an intermediatefield/frame in the second format, such that the pixel data occupies acontinuous active portion of the intermediate field/frame and the dummydata occupies the remainder of the intermediate field/frame; and meansfor processing the intermediate field/frame by expanding the activeportion thereof in the vertical and horizontal directions and producingan output field/frame in the second format such that the pixel dataextends across substantially the whole of the output field/frame in atleast one of the two directions.

The apparatus is of particular application in converting digital videosignals between formats having different aspect ratios, and in this casethe processing means may be arranged to be operable in a side-bar modeto expand the active portion of the intermediate field/frame to anextent such that the active portion extends across substantially thewhole of the output field/frame in one of the directions and such thatthe dummy data occupies at least one marginal portion of the outputfield/frame. Alternatively or additionally, the processing means may bearranged to be operable in an edge-crop mode to expand the activeportion of the intermediate field/frame to an extent such that theactive portion extends across substantially the whole of the outputfield/frame in one of the directions and across more than the outputfield/frame in the other direction so that at least one marginal portionof the active portion is cropped. Alternatively or additionally, theprocessing means may be arranged to be operable in a zoom mode to expandthe active portion of the intermediate field/frame to an extent suchthat the active portion extends across more than the whole of the outputfield/frame in one of the directions and across less than or more thanthe output field/frame in the other direction.

Preferably, the processing means is operable in the side-bar, edge-cropor zoom mode, as the case may be, to expand the intermediate field/framewith different horizontal and vertical expansions such that the ratio ofthe horizontal to vertical expansion is equal to the ratio of the pixelaspect ratio of the first format to that of the second format.Alternatively or additionally, the processing means may be arranged tobe operable in a titles mode to expand the active portion of theintermediate field/frame to an extent such that the active portionextends across substantially the whole of the output field/frame in bothof the directions without any substantial cropping of the activeportion. The processing means may include means to select operation inany one of the modes.

In one embodiment, in which the storage means can store a field/frame ofpixel data in the second format, and the storage control means includesmeans to select writing to and reading from the storage means and meansfor generating addresses for the storage means; the address generatingmeans is operable, (a) when writing is selected, to generate addressessequentially for the active portion of storage means corresponding to afield/frame in the first format, and (b) when reading is selected, togenerate addresses sequentially corresponding to a field/frame in thesecond format; and the storage means stores the dummy data at addressesnot in the active portion thereof.

In an alternative embodiment, in which the storage control meansincludes means to select writing to and reading from the storage means,and means for generating addresses for the storage means, the addressgenerating means is operable (a) when writing is selected, to generateaddresses sequentially for the field/frame of pixel data, and (b) whenreading is selected, to generate intermittently lines of addressescorresponding to lines of addresses of the field/frame in the firstformat. The storage control means is operable to output partial lines ofthe dummy pixel data between the generation of one line of addresses andthe next, and to output lines of the dummy pixel data between thegeneration of one field/frame of addresses and the next. This embodimenthas the advantage that the size of the storage means is related to thenumber of pixels in a field frame in the first format, rather than thelarger number of pixels in a field/frame in the second format.

In either of these embodiments, a further such storage means may beprovided, with the storage control means controlling the two storagemeans such that while one is being written to, the other is being readfrom, and vice versa. This has the advantage that, at least for sometypes of conversion, the apparatus can operate continuously.

Also, with any of these embodiments, the apparatus may be arranged sothat when writing of the, or one of the, storage means is selected, theaddresses for the storage means are generated at the pixel rate of thefirst format; and when reading of the, or one of the, storage means isselected, the addresses for that storage means are generated at thepixel rate of the second format. This enables realtime operation of theapparatus.

In accordance with another aspect of the present invention, there isprovided a method of up-converting a digital video signal from a firstdefinition format to a second high-definition format. The methodcomprises the steps of storing an input field/frame of pixel data in thefirst format; reading the stored pixel data interspersed with dummy dataas an intermediate field/frame in the second format, such that thepreviously stored pixel data occupies a continuous active portion of theintermediate field/frame and the dummy data occupies the remainder ofthe intermediate field/frame; and expanding the active portion of theintermediate field/frame in the vertical and horizontal directions andproducing an output field/frame in the second format such that thepreviously stored pixel data extends across substantially the whole ofthe output field/frame in at least one of the two directions.

In the case where the first and second formats have differentfield/frame aspect ratios, in the expansion step the active portion ofthe intermediate field/frame may be expanded in a side-bar mode to anextent such that the active portion extends across substantially thewhole of the output field/frame in one of the directions and such thatthe dummy data occupies at least one margin portion of the outputfield/frame. Alternatively, the active portion of the intermediatefield/frame may be expanded in an edge-crop mode to an extent such thatthe active portion extends across substantially the whole of the outputfield/frame in one of the directions and across more than the outputfield/frame in the other direction so that at least one marginal portionof the active portion is cropped. Alternatively, the active portion ofthe intermediate field/frame may be expanded in a zoom mode to an extentsuch that the active portion extends across more than the whole of theoutput field/frame in one of the directions and across less than or morethan the output field/frame in the other direction. In any of thesemodes, in the expansion step the intermediate field/frame is preferablyexpanded with different horizontal and vertical expansions such that theratio of the horizontal to vertical expansion is equal to the ratio ofthe pixel aspect ratio of the first format to that of the second format.Alternatively, the active portion of the intermediate field/frame may beexpanded in a titles mode to an extent such that the active portionextends across substantially the whole of the output field/frame in bothof the directions without any substantial cropping of the activeportion. The method may further comprise the step of selecting operationin any one of the above modes.

In one embodiment, the storing step includes the step of generating fora storage means addresses which are sequential for the field/frame ofpixel data in the first format; and the reading step includes the stepsof: generating for the storage means intermittently lines of addressescorresponding to lines of addresses int he first format; outputtingpartial lines of the dummy pixel data between the generation of one lineof addresses and the next; and outputting lines of the dummy pixel databetween the generation of one field/frame of addresses and the next. Inan alternative embodiment, the storing step includes the step ofgenerating for a storage means addresses which are sequential for anactive portion of storage means corresponding to a field/frame in thefirst format; the reading step includes the step of generating for thestorage means addresses which are sequential for a field/frame in thesecond format; and an initialisation step is provided in which the dummydata is stored at addresses in the storage means not in the activeportion thereof. In either of these embodiments, in the storing step,the addresses are preferably generated at the pixel rate of the firstformat; and in the reading step, the addresses are preferably generatedat the pixel rate of the second format.

The method preferably further comprises the step of addingsynchronisation data to the pixel data of the intermediate field/frame.

Other objects, features and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionof a preferred embodiment thereof, especially when considered with theaccompanying drawings in which like reference numerals are employed todesignate the same or similar components in the different figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic block diagram of an up-converter apparatus;

FIG. 2 illustrates various frames arising in the apparatus;

FIG. 3 is a block diagram of a format converter forming part of theapparatus of FIG. 1;

FIG. 4 is a block diagram of a system for up-converting a 525-lines 60field/s video signal to an 1125-lines 60 field/s digital format;

FIG. 5 is a block diagram of a system for up-converting a 625-lines 50field/s video signal to an 1125-lines 60 field/s digital format; and

FIG. 6 shows a modification to the system of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an apparatus is shown for up-converting an inputconventional definition CCIR 601 525-line format digital video signal oninput line 10 to an output high definition SMPTE 240 M format digitalvideo signal on output line 12. The input signal format is characterisedby 525 lines, 60 field/s, 2:1 interlaced, and each frame has an activearea of 720 (H) pixels×486 (V) pixels with a 4(H):3(V) frame aspectratio, as shown by the vertically hatched frame A in FIG. 2. It will beappreciated, therefore, that the input frame size is L×3L/4 (where L isthe width of the input frame). Also, each input pixel has an aspect of4/720(H):/486(V), or 9:10. It will be noted that the input pixels arenot square. The output signal format is characterised by 1125 lines, 60field/s, 2:1 interlaced, and each frame has an active area of 1920(H)pixels×1035(V) pixels with a 16(H):9(V) frame aspect ratio, as shown forexample by the vertically hatched portion of frame D in FIG. 2. It willbe appreciated that the output frame size is L'×9L'/16 (where L' is thewidth of the output frame). Also, each output pixel has an aspect ratioof 16/1920(H):9/1035(V), or 23:24. Thus, not only are the output pixelsnot square, but their aspect ratio is different to that of the inputpixels.

Each frame on line 10 is input to a format converter 14, which outputs acorresponding intermediate frame on line 16 to an imagetranslator/expander 18, which in turn outputs the output frame on line12. The intermediate frame on line 16 is of SMPTE 240 M format, but thepixel data of the input frame is contained in only part of theintermediate frame, for example in the top-left corner, as shown by thevertically hatched portion of frame B in FIG. 2, and has a size of3L'/8(H)×243L'/920(V) containing the 720(H)×486(V) pixels. The remainingdata in the intermediate frame B is dummy data, as shown by horizontalhatching.

In the translator/expanding 18, the pixel data of the intermediate frameB undergoes a translation of (t_(x), t_(y)), as shown for example byframe C and G in FIG. 2, and then undergoes an expansion about thecenter pixel of the frame at location (960, 518) by a factor of (e_(x),e_(y)), as shown for example by frames D, E, F and H in FIG. 2.

In the example shown by frame C, the translation (t_(x), t_(y)) is (600,275) which has the effect of placing the active pixel data (verticallyhatched) in the center of the frame.

From frame C, frame D is formed by an expansion (e_(x), e_(y)) of (8/3,230/81). The horizontal expansion of 8/3 has the effect of extending thewidth of the active area from 720 pixels to 1920 pixels, so that it isequal to the width of the frame. The vertical expansion of 230/81 hasthe effect of extending the height of the active area from 486 pixels to1380 pixels so that the aspect ratio of the image is returned to theoriginating value L':(1380/1035)×(9L'/16) or 4:3. However, this verticalexpansion also has the effect of extending the upper and lower marginalportions of the image outside of the frame D, and therefore thesemarginal portions, as shown by diagonal hatching above and below frameD, whose heights are each about 172 pixels, are cropped.

As an alternative, from face C, frame E is formed by an expansion(e_(x), e_(y)) of (2, 115/54). The vertical expansion of 115/54 has theeffect of extending the height of the active area from 486 pixels to1035 pixels, so that it is equal to the height of the frame. Thehorizontal expansion of 2 has the effect of extending the width of theactive area from 720 pixels to 1440 pixels so that the aspect ratio ofthe image is returned to the originating value of 1440L'/1920:9L'/16, or4:3. However, the horizontal expansion is not sufficient to cause theactive areas to extend completely across the frame E, and therefore leftand right marginal portions of the frame, whose widths are each 240pixels, are provided by the dummy data, as shown by the horizontalhatching in frame E.

It will be noted that some of the image has been lost from frame D,which may be acceptable in some cases, but not in others, and thatundesirable side bars are produced in frame E. In some cases, anexpansion between those for frames D and E may be acceptable, givingless lost image than frame D and narrower side bars than frame E. Fromframe C, frame F shows an expansion (e_(x), e_(y)) of (7/3, 805/324).The horizontal expansion of 7/3 has the effect of extending the width ofthe active area from 720 pixels to 1680 pixels, leaving side bars ofdummy data each 120 pixels wide. The vertical expansion of 805/324 hasthe effect of extending the height of the active area from 486 pixels to1207 pixels so that the aspect ratio of the image is returned to theoriginating value of 1680L'/1920:(1207/1035)×(9L'/16), or 4:3, and sothat top and bottom marginal portions of approximate heights of 86pixels each are cropped.

It is to be noted that for each of frames D, E and F, the ratio of thehorizontal expansion to the vertical expansion e_(x) /e_(y) is alwaysthe same and is 108/115. This is necessary in order not to distort theimage. The value e_(x) /e_(y) of 108/115 is derived from the ratio ofthe pixel aspect ratio of 9:10 for the CCIR 601 525-line format to thepixel aspect ratio of 23:24 for the SMPTE 240 M format, i.e.(9/10)/(23/24)=108/115.

There are cases in which distortion of the picture may be acceptable,for example when titles spread across substantially the whole of theinput frame on a relatively less significant background, and it isdesired not to lose any of the title information and also to avoid theproduction of any side bars in the output frame. In these and verticalexpansions are such as to cause the active area to extend horizontallyfrom 720 to 1920 pixels and vertically from 486 to 1035 pixels. Thus, anexpansion (e_(x), e_(y)) of (8/3, 115/54) is required, where thehorizontal expansion e_(x) is the same as for the edge-crop mode (frameD in FIG. 2) and the vertical expansion e_(y) is the same as for theside-bars mode (frame E in FIG. 2).

In the examples described so far, the translation (t_(x), t_(y))=(600,275) between frames B and C places the active area in the center offrame C, so that there is symmetrical cropping top and bottom in framesD and F, and so that there are symmetrical side bars left and right inframes E and F. In some cases, it may be desirable for the croppingand/or the side bars not to be symmetrical. Frames G and H show anexample where it it important for all of the bottom of the input imageto be included in the output image, but it does matter if the top iscropped, and it is desired not to have any side bars. In this case,frame G is formed by a translation of (t_(x), t_(y)) of (600, 214) (sothat the active portion of the frame G is higher in the frame than inthe case of frame C). Frame G then undergoes an expansion (e_(x), e_(y))of (8/3, 230/81) (which is similar to the expansion between frames C andD). However, because of the modified position of the active area inframe G, the active area in frame H extends exactly across the whole ofthe frame and extends to the bottom of the frame without cropping. Thetop marginal portion of the active area, 345 pixel high, is cropped, asindicated by the diagonal hatching. This is referred to as a zoom modeof operation.

In the above examples, the active area of the output frame is eitherless than the frame width (frame E and F), or is equal to it (frame Dand H). If desired, a greater horizontal expansion may be employed (thatis e_(x) may be greater than 8/3), so that the left and/or rightmarginal portions of the image, in addition to the upper and lowermarginal portions, are cropped in the output frame, and the translation(t_(x), t_(y)) may be chosen so that the desired portion of the inputimage appears in the output frame.

The above examples have considered the case of up-conversion from CCIR601 525-line format to SMPTE 240 M format. For the other formatsmentioned at the beginning of the specification, different translations(t_(x), t_(y)) and expansions (e_(x), e_(y)) will be required. For allthe formats considered, the size (P_(x), P_(y)) of the active portion ofthe frame, the frame aspect ratio R_(f), and the pixel aspect ratioR_(p) are as given in Table 1 below:

                  TABLE 1                                                         ______________________________________                                                   Active Pixels                                                                            Frame Aspect                                                                              Pixel Aspect                                FORMAT     (P.sub.x, P.sub.y)                                                                       Ratio (R.sub.f)                                                                           Ratio (R.sub.p)                             ______________________________________                                        SMPTE 240M (1920, 1035)                                                                             16/9        23/24                                       European HDTV                                                                            (1920, 1152)                                                                             16/9        16/15                                       CCIR 601   (720, 486) 4/3          9/10                                       525-line                                                                      CCIR 601   (720, 576) 4/3         16/15                                       625-line                                                                      4fsc D2 525-line                                                                         (768, 486) 4/3         27/32                                       4fsc D2 625-line                                                                         (948, 576) 4/3         64/79                                       ______________________________________                                    

It should be noted that the pixel aspect ratio is given by R_(p)=R_(f).P_(y) /P_(x).

The translation (t_(x), t_(y)) required to bring the active area of theintermediate frame to the center of the frame is given by (t_(x),t_(y))=((P_(x) "--P_(x) ')/2, (P_(y) "--P_(y) ')/2), where (P_(x) ',P_(y) ') and (P_(x) ", P_(y) ") are the sizes, in pixels, of the inputand output frames, respectively. Thus, for the possible conversionsconsidered here, the necessary translations are as given by Table 2below:

                  TABLE 2                                                         ______________________________________                                                          OUTPUT FORMAT                                               TRANSLATION TO CENTRE                                                                             SMPTE     European                                        (t.sub.x, t.sub.y)  240M      HDTV                                            ______________________________________                                        INPUT    CCIR 601 525-line                                                                            (600, 274)                                                                              (600, 333)                                  FORMAT   CCIR 601 625-line                                                                            (600, 229)                                                                              (600, 288)                                           4fsc D2 525-line                                                                             (576, 274)                                                                              (576, 333)                                           4fsc D2 625-line                                                                             (486, 229)                                                                              (486, 288)                                  ______________________________________                                    

The expansion (e_(x) ', e_(y) ') required to produce an output framejust with no side bars is given by (e_(x) ', e_(y) ')=((P_(x) "/P_(x)'), (P_(x) "R_(p) ")/ (P_(x) 'R_(p) ')), where R_(p) ' are the pixelaspect ratios for the input and output formats, respectively. Thus, forthe possible conversions considered here, the necessary expansions areas given by Table 3 below:

                  TABLE 3                                                         ______________________________________                                                        OUTPUT FORMAT                                                 EXPANSION (e.sub.x ', e.sub.y ')                                                                SMPTE       European                                        NO SIDE BARS      240M        HDTV                                            ______________________________________                                        INPUT   CCIR 601 525-line                                                                           (8/3, 230/81)                                                                             (8/3, 256/81)                               FORMAT  CCIR 601 625-line                                                                           (8/3, 115/48)                                                                             (8/3, 8/3)                                          4fsc D2 525-line                                                                            (5/2, 230/81)                                                                             (5/2, 256/81)                                       4fsc D2 625-line                                                                            (160/79, 115/48)                                                                          (160/79, 8/3)                               ______________________________________                                    

On the other hand, the expansion (e_(x) ", e_(y) ") required to producean output frame just with no cropping is given by (e_(x) ", e_(y)")=((P_(y) "R_(p) '), (P_(y) 'R_(p) "), (P_(y) "/P_(y) ')). Thus, forthe possible conversions considered here, the necessary expansions areas given by Table 4 below:

                  TABLE 4                                                         ______________________________________                                                        OUTPUT FORMAT                                                 EXPANSION (e.sub.x ", e.sub.y ")                                                                SMPTE       European                                        NO CROPPING       240M        HDTV                                            ______________________________________                                        INPUT   CCIR 601 525-line                                                                           (2, 115/54  (2, 64/27)                                  FORMAT  CCIR 601 625-line                                                                           (2, 115/64) (2, 2)                                              4fsc D2 525-line                                                                            (15/8, 115/54)                                                                            (15/8, 64/27)                                       4fsc D2 625-line                                                                            (120/79, 115/64)                                                                          (120/79, 2)                                 ______________________________________                                    

Also, the expansion (e_(x) ', e_(y) ") required to produce an outputframe in the titles mode is given by (e_(x) ', e_(y) ")=((P_(x) "/(P_(x)'), (P_(y) "/P_(y) ')). Thus, for the possible conversions consideredhere, the necessary expansions are as given by Table 5 below:

                  TABLE 5                                                         ______________________________________                                                        OUTPUT FORMAT                                                 EXPANSION (e.sub.x ', e.sub.y ")                                                                SMPTE       European                                        TITLES MODE       240M        HDTV                                            ______________________________________                                        INPUT   CCIR 601 525-line                                                                           (8/3, 115/54                                                                              (8/3, 64/27)                                FORMAT  CCIR 601 625-line                                                                           (8/3, 115/64)                                                                             (8/3, 2)                                            4fsc D2 525-line                                                                            (5/2, 115/54)                                                                             (5/2, 64/27)                                        4fsc D2 625-line                                                                            (160/79, 115/64)                                                                          (160/79, 2)                                 ______________________________________                                    

In the arrangement described above, the active area of the intermediateframe B is placed in the corner of the frame by the format converter 14,and the translator/expander 18 then moves the active area to, or near,the center of the frame (frames C and G) and then expands to active areafrom a center of expansion at the center of the frame.

In one alternative arrangement, the active area of the frame B may bedirectly placed by the format converter 14 in the center of the frame.Thus, a frame like frame C in FIG. 2 is directly produced, and notranslation, as opposed to expansion, is required to produce the framesD, E and F with symmetrical cropping, side bars, or other effects. Inorder to produce and asymmetrical frame line frame G, a small amount oftranslation would need to be provided by the translator/expander 18.

In another alternative arrangement, the active portion of theintermediate frame is placed in a corner or the frame, as shown by frameB in FIG. 2, but the transplator/expander 18 does not separatelytranslate and expand the active portion. Instead, thetranslator/expander 18 expands the active area from a center ofexpansion which does not coincide with the center of the frame. Forexample, if frame B as shown in FIG. 2 were expanded with (e_(x),E_(y))=(8/3, 230/81) from a center of expansion at the top-left cornerof the frame, the result would be as shown by frame H, except that thecropped marginal portion would be at the bottom, rather than the top, ofthe frame.

As shown in FIG. 1, the format converter 14 and translator/expander 18are controlled by a system controller 20 which provides signals to theconverter 14 and translator/expander 18 controlling: the input andoutput formats: the translation and expansion provided by thetranslator/expander 18; and the value of the dummy data. As analternative, these parameters may be manually set directly, preset, orhand-wired.

Referring now to FIG. 3, further detail of the format converter 14 isshown. The input signal on line 10 is fed to a controllable data inputswitch 22 and to a synchronisation decoder 24 which detects thehorizontal and vertical synchronisation signals in the input signals andsupplied timing signals to a selector circuit 26, to write and readaddress generators 34,40, and to a synchronisation formatter 28 whichadds synchronisation signals to the output signal on line 16. Theselector 26 controls the data input switch 22 to route the incomingpixel data either to the data input of one field store 30₀ or to thedata input of another field store 30₁. The selector 26 also controls acontrollable write address switch 32 to route write addresses from thewrite address generator 34 to the address input of the same field store30₀ or 30₁. The converter 14 also includes a controllable data outputswitch 36 under control of the selector circuit 26, which is controlledto route data read from the field store 30₀ or 30₁, which is not beingwritten to, to the line 16. The selector circuit 26 also controls acontrollable read address switch 38 to route read addresses from theread address generator 40 to the address input of the field store 30₀ or30₁, which is being read. The selector circuit also supplies read/writeenable control signals to the field stores 30₀, 30₁. The addressgenerators 34,40 and the selector circuit 26 also receive controlsignals from the system controller indicative of the type of inputsignal format and of the required type of output signal format.

FIG. 3 is a schematic drawing to assist in illustrating the pixel dataflow and the address data flow. In practice, the data input switch 22may be omitted and the input line 10 may be directly connected to thefield stores 30₀, 30₁, because each field store will ignore input dataon line 10 when reading is selected. Also, the field stores may havetri-state outputs, in which case the data output switch 36 is redundant.Furthermore, the address switches 32, 38 may be omitted if the fieldstores have separate inputs for wire addresses and read addresses.

The operation of the format converter of FIG. 3 will now be describedfor conversion from 4fsc D2 525-line format to SMPTE 240 M format. Aseach input frame arrives on line 10, the odd field of the frame iswritten to the field store 30₀, and the even field is then written tothe field store 30₁. While the odd field is being written to the fieldstore 30₀, the even field of the preceding frame is being read from thefield store 30₁ and output on line 16, and while the even field of eachframe is being written to the field store 30₁, the odd field of the sameframe is being read from the field store 30₀ and output on line 16.

The input pixels arrive at a rate of 14.3 MHz (which is four times theNTSC sub-carrier frequency) and accordingly, for writing, the writeaddress generator 34 produces sequential write addresses (p_(x), p_(y))at that rate. The write addresses for an even field of a frame incrementin the fashion shown in Table 6 below:

                                      TABLE 6                                     __________________________________________________________________________    (0, 0)                                                                              (1, 0)                                                                             (2, 0)                                                                              (3, 0)                                                                             . . .                                                                             (718, 0)                                                                           (719, 0)                                       (0, 2)                                                                              (1, 2)                                                                             (2, 2)                                                                              (3, 2)                                                                             . . .                                                                             (718, 2)                                                                           (719, 2)                                       (0, 4)                                                                              (1, 4)                                                                             (2, 4)                                                                              (3, 4)                                                                             . . .                                                                             (718, 4)                                                                           (719, 4)                                       .     .    .     .    . . .                                                                             .    .                                              .     .    .     .        .    .                                              .     .    .     .        .    .                                               (0, 484)                                                                            (1, 484)                                                                           (2, 484)                                                                            (3, 484)                                                                          . . .                                                                             (718, 484)                                                                         (719, 484)                                     __________________________________________________________________________

Somewhat, similarly, the write addresses for an odd field of a frameincrement in the fashion shown in Table 7 below:

                                      TABLE 7                                     __________________________________________________________________________    (0, 1)                                                                              (1, 1)                                                                             (2, 1)                                                                              (3, 1)                                                                             . . .                                                                             (718, 1)                                                                           (719, 1)                                       (0, 3)                                                                              (1, 3)                                                                             (2, 3)                                                                              (3, 3)                                                                             . . .                                                                             (718, 3)                                                                           (719, 3)                                       (0, 5)                                                                              (1, 5)                                                                             (2, 5)                                                                              (3, 5)                                                                             . . .                                                                             (718, 5)                                                                           (719, 5)                                       .     .    .     .    . . .                                                                             .    .                                              .     .    .     .        .    .                                              .     .    .     .        .    .                                               (0, 485)                                                                            (1, 485)                                                                           (2, 485)                                                                            (3, 485)                                                                          . . .                                                                             (718, 485)                                                                         (719,485)                                      __________________________________________________________________________

The output pixels need to be produced at a pixel rate of 74.25 MHz, anddummy pixel data need to be produced for the latter part of each lineand for the latter part of each field. The dummy data may be producedeither by pre-storing a dummy data element at one particular location ineach field store 30₀, 30₁, for example at (0, 486) and by pointing tothat location whenever dummy data is to be output. Alternatively, fieldstores 30₀, 30₁ may be employed which each have a capacity of one fieldin the high definition format (i.e. 1920 pixels ×1035 pixels for SMPTE240 M format) and dummy data may be pre-stored in that part of eachfield store 30₀, 30₁ to which the input data is not written.

In the first case, the read addresses provided by the read addressgenerator 40 would be incremented in the fashion shown in Table 8 belowfor the even field of each frame:

                                      TABLE 8                                     __________________________________________________________________________    (0, 0)                                                                              (1, 0)                                                                              . . .                                                                             (718, 0)                                                                             (719, 0)                                                                             (0, 486) × 1200                           (0, 2)                                                                              (1, 2)                                                                              . . .                                                                             (718, 2)                                                                             (719, 2)                                                                             (0, 486) × 1200                           (0, 4)                                                                              (1, 4)                                                                              . . .                                                                             (718, 4)                                                                             (719, 4)                                                                             (0, 486) × 1200                           .     .     . . .                                                                             .      .      .                                               .     .         .      .      .                                               .     .         .      .      .                                                (0, 484)                                                                            (1, 484)                                                                           . . .                                                                              (718, 484)                                                                           (719, 484)                                                                          (0, 486) × 1200                           (0, 486) × 528000                                                       __________________________________________________________________________

Somewhat similarly, the read addresses provided by the read addressgenerator 40 would be incremented in the fashion shown in Table 9 belowfor the odd field of each frame:

                                      TABLE 9                                     __________________________________________________________________________    (0, 1)                                                                              (1, 1)                                                                              . . .                                                                             (718, 1)                                                                             (719, 1)                                                                             (0, 486) × 1200                           (0, 3)                                                                              (1, 3)                                                                              . . .                                                                             (718, 3)                                                                             (719, 3)                                                                             (0, 486) × 1200                           (0, 5)                                                                              (1, 5)                                                                              . . .                                                                             (718, 5)                                                                             (719, 5)                                                                             (0, 486) × 1200                           .     .     . . .                                                                             .      .      .                                               .     .         .      .      .                                               .     .         .      .      .                                                (0, 485)                                                                            (1, 485)                                                                           . . .                                                                              (718, 485)                                                                           (719, 485)                                                                          (0, 486) × 1200                           (0, 486) × 526080                                                       __________________________________________________________________________

In the second case, the read addresses provided by the read addressgenerator 40 would be incremented in the fashion shown in Table 10 belowfor the even field of each frame:

                                      TABLE 10                                    __________________________________________________________________________    (0, 0)                                                                              (1, 0)                                                                              . . .                                                                            (719, 0)                                                                             (720, 0)                                                                             . . .                                                                            (1919, 0)                                     (0, 2)                                                                              (1, 2)                                                                              . . .                                                                            (719, 2)                                                                             (720, 2)                                                                             . . .                                                                            (1919, 2)                                     (0, 4)                                                                              (1, 4)                                                                              . . .                                                                            (719, 4)                                                                             (720, 4)                                                                             . . .                                                                            (1919, 4)                                     .     .     . . .                                                                            .      .      . . .                                                                            .                                             .     .        .      .         .                                             .     .        .      .         .                                             (0, 484)                                                                            (1, 484)                                                                            . . .                                                                             (719, 484)                                                                           (720, 484)                                                                          . . .                                                                            (1919, 484)                                   (0, 486)                                                                            (1, 486)                                                                            . . .                                                                            . . .  . . .  . . .                                                                            (1919, 486)                                   .     .     . . .                                                                            . . .  . . .  . . .                                                                            .                                             .     .                         .                                             .     .                         .                                              (0, 1034)                                                                           (1, 1034)                                                                          . . .                                                                            . . .  . . .  . . .                                                                             (1919, 1034)                                 __________________________________________________________________________

Somewhat similarly, the read addresses provided by the read addressgenerator 40 would be incremented in the fashion shown in Table 11 belowfor the odd field of each frame:

                                      TABLE 11                                    __________________________________________________________________________    (0, 1)                                                                              (1, 1)                                                                              . . .                                                                            (719, 1)                                                                             (720, 1)                                                                             . . .                                                                            (1919, 1)                                     (0, 3)                                                                              (1, 3)                                                                              . . .                                                                            (719, 3)                                                                             (720, 3)                                                                             . . .                                                                            (1919, 3)                                     (0, 5)                                                                              (1, 5)                                                                              . . .                                                                            (719, 5)                                                                             (720, 5)                                                                             . . .                                                                            (1919, 5)                                     .     .     . . .                                                                            .      .      . . .                                                                            .                                             .     .        .      .         .                                             .     .        .      .         .                                             (0, 485)                                                                            (1, 485)                                                                            . . .                                                                             (719, 485)                                                                           (720, 485)                                                                          . . .                                                                            (1919, 485)                                   (0, 487)                                                                            (1, 487)                                                                            . . .                                                                            . . .  . . .  . . .                                                                            (1919, 487)                                   .     .     . . .                                                                            . . .  . . .  . . .                                                                            .                                             .     .                         .                                             .     .                         .                                              (0, 1033)                                                                           (1, 1033)                                                                          . . .                                                                            . . .  . . .  . . .                                                                             (1919, 1033)                                 __________________________________________________________________________

In the above tables, the addresses to the right of, and/or below, thedashed lines contain the dummy data.

Also, in the above tables, the addresses relate to pixel positions inthe picture, but the RAMs of the field stores need not necessarily beorganised in this manner, and a conversion may be made between the pixeladdress and the RAM address. For example, when the scheme of Tables 8and 9 is used, the RAM address A for the even and odd field stores maybe obtained as:

    A=P.sub.x +(1024p.sub.y /2)--even

    A=P.sub.x +(1024(p.sub.y -1)/2)--odd.

In the case where p_(y) is represented as a 9-bit number p_(y8) top_(y0), and p_(x) is represented as a 10-bit number p_(x9) to p_(x0),this conversion can be simply accomplished by supplying the mostsignificant eight bits p_(y8) to p_(y1) of p_(y) as the most significanteight bits A₁₇ to A₁₀ of the RAM address A and supplying the ten bitsp_(x9) to p_(x0) of p_(x) as the least significant ten bits A₉ to A₀ ofthe RAM address A. Thus, in this case the RAM of each field store 30₀,30₁ needs to have a capacity of 2¹⁸, or 256 kB. If the apparatus is tobe able to convert from CCIR 601 625-line format, or 4 fsc 625 D2format, for each of which there are 288 pixels vertically in a field,then p_(y) may be represented by a 10-bit number p_(y9) to p_(y0), ofwhich nine bits p_(y9) to p_(y1) are used, and in this case each fieldstore 30₀, 30₁ will need to have a capacity of 2¹⁹, or 0.5 MB.

In the case of the scheme of Tables 10 and 11, the RAM address A for theeven and odd field stores may be obtained as:

    A=p.sub.x +(2048p.sub.y /2)--even

    A=p.sub.x +(2048(p.sub.y -1)/2)--odd.

In the case where p_(y) and p_(x) are each represented as 11-bit numbersp_(y10) to p_(y0) and p_(x10) to p_(x0), this can conversion can besimply accomplished by supplying the most significant ten bits p_(y10)to p_(y1) of p_(y) as the most significant ten bits A₂₀ to A₁₁ of theRAM address A and supplying the eleven bits p_(x10) to p_(x0) of p_(x)as the least significant eleven bits A₁₀ to A₀ of the RAM address A.Thus, in the case the RAM of each field store 30₀, 30₁ needs to have acapacity of 2²¹, or 2MB.

It should be noted that other forms of conversion may be made betweenthe pixel addresses and RAM addresses, or the address generators 34, 40may be designed to generate addresses which can be directly used by thefield stores 30₀, 30₁.

It will be appreciated that the dummy data appears, in some cases, inthe frames output from the translator/expander 18, for example in theframes E and F shown in FIG. 2. Therefore, the dummy data is preferablychosen to provide a background colour, such as black, or even abackground pattern in the second case given above. To this end, in aninitialisation procedure of the format converter 14, the data inputswitch 22 may be moved to third and fourth positions (not shown) toroute background pixel data from the system controller 20 to the firstand second field stores 30₀, 30₁, with the write address generator 34being controlled to generate the address (0, 486) in the first casementioned above, or to generate all of the required background dataaddresses 720<=p_(x) 21 1919 and/or 486<p_(y) <1034 in the second casementioned above. If this is done, then the active area of the frame B(FIG. 2) is preferably placed by the format converter 14 in the centerof the frame.

FIG. 4 shows a system configuration, employing the apparatus describedabove, for conversion from 525 lines 60 field/s conventional definitionformat to 1125 lines 60 field/s high definition format. The conventionaldefinition digital signal is supplied via line 10 to the formatconverter 14 selectively from a conventional definition digital videotape recorder (DVTR) 42, from other digital sources on line 44, or froman analogue video tape recorder (AVTR) 46 via an analogue-to-digitalconverter 48. The intermediate high definition frames output from theformat converter 14 on line 16 may selectively be supplied directly tothe translator/expander 18, or via a high definition DVTR (HDDVTR) 50.The frames output from the translator/expander 18 on line 12 may besupplied to an HDDVTR 52 or elsewhere. In addition to controlling theformat converter 14 and the translator/expander 18, the systemcontroller 20 also controls the input DVTR 42, the input AVTR 46, theintermediate HDDVTR 50 and the output HDDVTR 52 to set tape start andstop positions, etc.

In the conversion from CCIR 601 525-lines format or 4 fsc 525-linesformat to SMPTE 240 M format, or from CCIR 601 625-lines format or 4 fscD2 625-lines format to European HDTV format, there is no substantialchange in field or frame rate, and therefore temporal conversion doesnot need to be considered. (Although the proper field rate of an NTSCsignal is 0.1% slow than 60 Hz, that is 59.94 Hz, the converter is runoff-line, and therefore the input and output can be both locked at 60 Hzor 59.94 Hz without any adverse effects.) in some cases of conversionfrom an input format of 50 field/s 2:1 interlaced to an output format of60 field/s 2:1 interlaced, or vice versa the need for temporalconversion may be ignored, for example if the source material is astatic image, such as a still background, or static title. However, inother cases, temporal conversion does need to be taken into account.Nevertheless, in the case of source material such as scrolling titles, apanned background, or computer generated scenes, the movement in thesource material can be generated at a rate 5/6 slower, or 6/5 fasterthan the movement required in the output material and thus providetemporal conversion a priori.

FIG. 5 shows a system configuration, employing the apparatus describedabove, for conversion from 625 lines 50 field/s conventional definitionformat to 1125 lines 60 field/s high definition format. Asa in the caseof FIG. 4, the conventional definition digital signal is supplied vialine 10 to the format converter 14 selectively from a conventionaldefinition digital video tape recorder (DVTR) 42, from other digitalsources on line 44, or from an analogue video tape recorder (AVTR) 46via an analogue-to-digital converter 48. The intermediate highdefinition frame is output from the format converter 14 on line 16' viaa high definition digital frame recorder (HDDFR) 54 to an HDDVTR 56. Ina first phase of operation, the part of the system of FIG. 5 describedso far is operated in a burst intermittent mode, that is to say a burstof input frames pass from the selected source via the format converter14 to the HDDFR 54 at the source 50 field/s rate, and then theintermediate frame stored in the HDDFR 54 are output at 60 field/s tothe HDDVTR 56 which records at normal speed. This procedure is repeateduntil all of the source material has been converted. Then, in a secondstage of operation, the intermediate frame recorded by the HDDVTR 56 areplayed back at normal speed and supplied on line 16" to thetranslator/expander 18 and then to the output HDDVTR 52 or elsewhere.

In one modification to the system of FIG. 5, the HDDFR 54 may bereplaced by a pair of HDDFRs and a multiplexer operated under control ofthe system controller 20 such that while one burst of frames is beingoutput to the HDDVTR 56 by one of the HDDFRs, the next burst of framescan be recorded by the other HDDFR and vice versa. This enables the DVTR42 to play continuously and the converter 14 to convert continuously inthe case of conversion frame a 50 field/s conventional definition formatto a 60 field/s high definition format. Alternatively, it enables theHDDVTR 56 to record continuously in the case of conversion from a 60field/s conventional definition format to a 50 field/s high definitionformat. These effects may also be obtained by suing an HDDFR 54 whichcan play and record different fields simultaneously.

In another modification of the system of FIG. 5, as shown in FIG. 6, aconventional definition digital frame recorder (CDDFR) 54' may be placedupstream of the format converter 14, instead of HDDFR 54 downstream ofthe format converter 14. In this case, a burst of input frames are inputfrom the selected source to the CDDFR 54' at the source 50 field/s rate,and then the frames stored in the CDDFR' are output at 60 field/s viathe format converter 14 to the HDDVTR 56 which records at normal speed.As with the FIG. 5 arrangement, this procedure is repeated until all ofthe source material has been converted. In other respects, the system ofFIG. 6 is similar to that of FIG. 5. Accordingly, in one modificationsto the system of FIG. 6, the CDDFR 54' may be replaced by a pair ofCDDFRs and a multiplexer operated under control of the system controller20 such that while one bust of frames is being output to the formatconverter 14 by one of the CDDFRs, the next burst of frames can berecorded by the other CDDFR and vice versa.

As an alternative to using the HDDFR 54 (FIG. 5), or the CDDFR 54' (FIG.6), an HDDVTR 56 may be employed which is operable in a stunt mode suchthat it records at 50 field/s and plays back at 60 field/s. The HDDFR 54(FIG. 5) may be provided by a Sony HDDF-500. The translator/expander 18may be implemented by a known digital video effects unit (also known asa digital multi effects unit), which, in known manner, can manipulate afield of digital video data to provide effects such as expansion,contraction, panning, clipping and partial overwriting. In thisconnection reference is directed, for example to K. Blair Benson,"Television Engineering Handbook", McGraw-Hill Book Company, New York,1986, Chapter 14, the content of which is incorporated herein. Thesystem controller may be implemented using an edite controller such asthe Sony VBE 9000.

It will be appreciated than many modifications and developments may bemade to the apparatus, system and method described above.

For example, the description above has considered video signal formatswhich are b 2:1 interlaced, but the invention is equally applicable toprogressive scan originated material. In order to maintain resolutionand data rate, the stores 30₀, 30₁ need in this case to be able to storea whole frame of video signal, rather than one field. Alternatively, thesame capacity stores as mentioned above may be used, with a reduced datarate and consequent reduced resolution.

Having described a preferred embodiment of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to the precise embodiment and that various changes andmodifications thereof may be effected by one skilled in the art withoutdeparting from the spirit or scope of the invention as defined in theappended claims.

What is claimed is:
 1. An apparatus for up-converting a digital video signal from a first definition format to a second high-definition format, comprising:storage means for storing an input field/frame of pixel data in the first format; storage control means for controlling the storage means to output the stored pixel data together with dummy data as an intermediate field/frame in the second format, such that the pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; and means for processing the intermediate field/frame by expanding the active portion thereof in the vertical and horizontal directions and producing an output field/frame in the second format such that the pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
 2. An apparatus as claimed in claim 1, wherein:the first and second formats have different field/frame aspect ratios; and the processing means is operable in a side-bar mode to expand the action portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and such that the dummy data occupies at least one marginal portion of the output field/frame.
 3. An apparatus as claimed in claim 1, wherein:the first and second formats have different field/frame aspect ratios; and the processing means is operable in an edge-crop mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across more than the output field/frame in the other direction so that at least one marginal portion of the active portion is cropped.
 4. An apparatus as claimed in claim 1, wherein:the first and second formats have different field/frame aspect ratios; and the processing means is operable in a zoom mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across more than the whole of the output field/frame in one of the directions and across less than or more than the output field/frame in the other direction.
 5. An apparatus as claimed in any of claims 2 to 4, wherein the processing means is operable in the side-bar, edge crop or zoom mode, as the case may be, to expand the intermediate field/frame with different horizontal and vertical expansions such that the ratio of the horizontal to vertical expansion is equal to the ratio of the pixel aspect ratio of the first format to that of the second format.
 6. An apparatus as claimed in claim 1, wherein:the first and second formats have different field/frame aspect ratios; and the processing means is operable in a titles mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in both of the directions without any substantial cropping of the active portion.
 7. An apparatus as claimed in claim 6, wherein:said means for processing is selectively operable in a side-bar mode to expand the active portion of the intermediate field/frame to an extend such that the active portion extends across substantially the whole of the output field/frame in one of said directions and such that the dummy data occupies at least one marginal portion of the output field/frame, in an edge-crop mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across substantially the whole of the output field/frame in one of said directions and across more than the output field/frame in the other of said directions so that at least one marginal portion of the active portion is cropped, and in a zoom mode to expand the active portion of the intermediate field/frame to an extent such that the active portion extends across more than the whole of the output field/frame in one of said directions and across less than or more than the output field/frame in the other of said directions; and said means for processing includes means for selecting operation in any one of said side-bar, edge-crop, zoom and titles modes.
 8. An apparatus as claimed in claim 1, wherein the storage control means includes means for adding synchronisation data to the pixel data of the intermediate field/frame.
 9. An apparatus for up-converting a digital video signal from a first definition format to a second higher-definition format, comprising:storage means having a writing mode for storing an input field/frame of pixel data in the first format and a reading mode; storage control means for controlling said storage means in said reading mode to output the stored pixel data together with dummy data as an intermediate field/frame in the second format, such that the pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; said storage control means including means for selecting one of said writing and reading modes of the storage means, and means for generating addresses for the storage means; said means for generating addresses being operable when said writing mode is selected to generate addresses sequentially for the field/frame of pixel data, and when said reading mode is selected to generate addresses sequentially for the field/frame of pixel data, and when said reading mode is selected to generate intermittently lines of addresses corresponding to lines of addresses in the first format; the storage control means being operable to output partial lines of the dummy pixel data between the generation of one line of addresses and the next, and to output lines of the dummy pixel data between the generation of one field/frame of addresses and the next; and means for processing the intermediate field/frame by expanding the active portion thereof in the vertical and horizontal directions and producing an output field/frame in the second format such that the pixel data extends across substantially the whole of the output field/frame in at least one of said directions;
 10. An apparatus as claimed in claim 9, wherein a further such storage means is provided, and the storage control means controls the two storage means such that while one is being written to, the other is being read from, and vice versa.
 11. An apparatus as claimed in claim 9, wherein:wherein writing of the, or one of the, storage means is selected, the addresses for that storage means are generated at the pixel rate of the first format; and when reading of the, or one of the, storage means is selected, the addresses for the storage means are generated at the pixel rate of the second format.
 12. An apparatus for up-converting a digital video signal from a first definition format to a second higher-definition format, comprising:storage means for selectively storing a field/frame of pixel data in the first format and in the second format; storage control means for controlling the storage means to output the stored pixel data together with dummy data as an intermediate field/frame in the second format, such that the pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; said storage control means including means for selecting one of said writing and reading modes of the storage means, and means for generating addresses for the storage means; said means for generating addresses being operable when said writing mode is selected to generate addresses sequentially for the active portion of said storage means corresponding to a field/frame in the first format, and when said reading mode is selected to generate addresses sequentially corresponding to a field/frame in the second format; the storage means storing the dummy data at addresses not in the active portion thereof; and means for processing the intermediater field/frame by expanding the active portion thereof in the vertical and horizontal directions and producting an output field/frame in the second format such that the pixel data extends across substantially the whole of the output field/frame in at least one of said directions.
 13. A method of up-converting a digital video signal from a first definition format to a second higher-definition format, comprising the steps of:storing an input field/frame of pixel data in the first format; reading the stored pixel data interspersed with dummy data as an intermediate field/frame in the second format, such that the previously stored pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame; and expanding the active portion of the intermediate field/frame in the vertical and horizontal directions and producing an output field/frame in the second format such that the previously stored pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
 14. A method as claimed in claim 13, for use in the case where the first and second formats have different field/frame aspect ratios, wherein in the expansion step the active portion of the intermediate field/frame is expanded in a side-bar mode to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and such that the dummy data occupies at least one marginal portion of the output field/frame.
 15. A method as claimed in claim 13, for use in the case where the first and second formats have different field/frame aspect ratios, wherein in the expansion step the active portion of the intermediate field/frame is expanded in an edge-crop mode to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across more than the output field/frame in the other direction so that at least one marginal portion of the active portion is cropped.
 16. A method as claimed in claim 13, for use in the case where the first and second formats have different field/frame aspect ratios, wherein in the expansion step the active portion of the intermediate field/frame is expanded in an edge-crop mode to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across less than or more than the output field/frame in the other direction.
 17. A method as claimed in any of claim 14 to 16, wherein in the expansion step the intermediate field/frame is expanded with different horizontal and vertical expansions such that the ratio of the horizontal to vertical expansion is equal to the ratio of the pixel aspect ratio of the first format to that of the second format.
 18. A method as claimed in claim 13, for use in the case where the first and second formats have different field/frame aspect ratios, wherein in the expansion step the active portion of the intermediate field/frame is expanded in a title mode to an extent such that the active portion extends across substantially the whole of the output field/frame in both of the directions without any substantial cropping of the active portion.
 19. A method as claimed in claim 18 wherein:in a side-bar mode the active portion of the intermediate field frame is expanded in the expansion step to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and such that the dummy data occupies at least one marginal portion of the output field/frame; in an edge-crop mode the active portion of the intermediate field/frame is expanded in the expansion step to an extent such that the active portion extends across substantially the whole of the output field/frame in one of the directions and across more than the output field/frame in the other direction so that at least one marginal portion of the active portion is cropped; and in a zoom mode the active portion of the intermediate field/frame is expanded in the expansion step to an extent such that the active portion extends across more than the whole of the output field/frame in one of the directions and across less than or more than the output field/frame in the other directions; and further comprising the step of selecting operation in any one of said side-bar, edge-crop, zoom and titles modes.
 20. A method as claimed in claim 13, further comprising the step of adding synchronisation data to the pixel data of the intermediate field/frame.
 21. A method of up-converting a digital video signal from a first definition format to a second higher-definition format, comprising the steps of:storing an input field/frame of pixel data in the first format, said storing including the step of generating for a storage means addresses which are sequential for the field/frame of pixel data for the first format; reading the stored pixel data interspersed with dummy data as an intermediate field/frame in the second format, such that the previously stored pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame, said reading including the steps of:generating intermittently for the storage means lines of addresses corresponding to lines of addresses in the first format, outputting partial lines of the dummy pixel data between the generation of one line of address and the next; and outputting lines of the dummy pixel data between the generation of one field/frame of addresses and the next; and expanding the active portion of the intermediate field/frame in the vertical and horizontal directions and producing an output field/frame in the second front such that the previously stored pixel data extends across substantially the whole of the output field/frame in at least one of the two directions.
 22. A method as claimed in claim 20, wherein:in the storing step, the addresses are generated at the pixel rate of the first format; and in the reading step, the addresses are generated at the pixel rate of the second format.
 23. A method of up-converting a digital video signal from a first definition format to a second higher-definition format, comprising the steps of:initializing a storage means by storing dummy data at addresses in the storage means not in an active portion thereof corresponding to a field/frame in the first format; storing an input field/frame of pixel data in the first format, said storing including the step of generating for the storage means addresses which are sequential for the active portion of the storage means reading the stored pixel data interspersed with the dummy data as an intermediate field/frame in the second format, such that the previously stored pixel data occupies a continuous active portion of the intermediate field/frame and the dummy data occupies the remainder of the intermediate field/frame, said reading including the step of generating for the storage means addresses which are sequential for a field/frame in the second format; and expanding the active portion of the intermediate field/frame in the vertical and horizontal directions and producing an output field/frame in the second format such that the previously stored pixel data extends across substantially the whole of the output field/frame in at least one of the two directions. 